The present invention relates to a ribbon feed mechanism for use in a printer, a typewriter or the like.
FIGS. 1 and 2 of the accompanying drawings illustrate a printer by way of example which incorporates a ribbon feed mechanism therein. More specifically, a carriage 2 is movably mounted on a frame 1 and supports thereon a wire-dot head 3 and a ribbon cassette 4 with a ribbon 5 wound therein, the ribbon 5 including an exposed stretch disposed in confronting relation to a platen 6. The carriage 2 with the ribbon cassette 4 mounted thereon is moved by a wire rope or the like (not shown) laterally along the platen 6 on the frame 1. Since the wire-dot head 3 can print desired characters or the like while it moves in opposite directions, the carriage 2 is shifted one step to the left or right each time one character is printed, and the ribbon 5 is fed along in one direction to bring an unused section of the ribbon 5 to a print position in front of the wire-dot head 3.
One conventional ribbon feed mechanism to be incorporated in the above printer is illustrated in FIGS. 3 and 4 of the accompanying drawings. A pair of upper and lower one-way clutches 14, 15 is mounted on a ribbon drive shaft 11. A pair of upper and lower pulleys 12, 13 is force-fitted over the outer peripheries of the one-way clutches 14, 15, respectively, with parallel wire ropes 16, 17 having single opposite turns wound around the pulleys 12, 13, respectively. When the wire rope 16 is pulled to the right to move the ribbon feed mechanism to the right, the upper pulley 12 and one-way clutch 14 rotate clockwise (FIG. 3) in unison. At this time, the one-way clutch 14 transmits driving power to rotate the ribbon drive shaft 11 clockwise about its own axis. The lower pulley 13 and one-way clutch 15 are rotated counterclockwise, during which time the one-way clutch 15 is disconnected to transmits no driving power to the ribbon drive shaft 11. Conversely, when the wire rope 17 is pulled to the left to move the ribbon feed mechanism to the left, the lower pulley 12 and one-way clutch 15 rotate clockwise in unison to rotate the ribbon drive shaft 11 clockwise about its own axis. The upper pulley 12 and one-way clutch 14 are rotated counterclockwise, whereupon the one-way clutch 14 remains disconnected. Accordingly, the ribbon drive shaft 11 rotates in one direction only as shown in FIG. 3 at all times when the ribbon feed mechanism is moved in different directions.
The conventional ribbon feed mechanism thus constructed is disadvantageous in that it must employ two expensive one-way clutches, and it is time-consuming and requires an increased number of assembling steps to train the wire ropes 16, 17 around the pulleys 12, 13, resulting in an increased cost of manufacture of the overall mechanism.